This invention is related generally to electronic circuits used in data paths of mass storage devices, particularly those employed as part of rotating magnetic disk memory systems.
As is well known, rotating disk storage devices magnetically record bits of data in concentric tracks on magnetic surfaces of one or more rotating disks. A read/write head is provided for each such disk surface. A mechanism is provided for moving the disk heads radially inward and outward to position them over the desired track for reading or writing data on such a track. Such data is recorded in sectors that each contain a set maximum number of bytes of data plus identification information, error correction codes, and various other control and status bits.
In order to shrink the size of the disk and increase the amount of data that can be stored in such systems, a great deal of effort has been directed toward increasing the density of bits recorded around each track, and toward reducing the distance between the tracks so that more of them can be included on a given surface area. The density of bits stored on each track is made to be roughly the same, resulting in the rate of data written to or read from the disk being higher on outer tracks than on the inner tracks. Rather than the data rate being different for each track, the tracks are generally grouped into zones of tracks with the bit density on each track within a given zone varied so that the bit rate is the same when reading from or writing to any track within a given zone. In order to finally position the head over desired track, and thus allow the tracks to be packed closer together, groups of head positioning data bits, commonly called servo bursts, are permanently recorded at spaced intervals around each track and interleaved with data recorded on the tracks. The servo signals including such bursts are read by the read/write head during both read and write operations in order to precisely position the head over the track.
The electronics used in a magnetic disk storage system include a microprocessor based controller that operates in response to commands from a host computer to position the read/write heads over designated tracks in a manner to transfer data files between the disk and the host computer. Data path electronics are also made a part of the disk storage system for both reading data from and writing data to the disk. In the read path, a preamplifier is generally connected directly to the head, with the amplified analog signal read from the disk being applied to a pulse detector, a circuit to separate the clock signal from the data, a decoder, and the like. In the write data path, at least an encoder is employed.
In order to improve the signal-to-noise ratio, the analog portion of the read path electronics commonly includes a low pass filter. The frequency cutoff of the filter is set to allow the bandwidth of the recorded data to pass through without attenuation while severely attenuating higher frequencies where troublesome noise can occur. More recently, such a filter has become available which has a variable cutoff frequency that is set by an electrical signal. This allows the pass band of the filter to be adjusted to conform to the different bandwidths in the various track zones where the data rates are different. An example of a controllable cutoff low pass filter is given in a patent application of Petersen et al., entitled "Digitally Programmable Linear Phase Filter Having Phase Equalization", filed Jul. 31, 1991, and assigned Ser. No. 07/739,015, now U.S. Pat. No. 5,245,565 which is incorporated herein in its entirety by this reference. Currently available data path filters are separate integrated circuit chips with essentially no other functions included on them. The variable cutoff frequency filter described above is available from IMP, Inc. assignee of the present application, under part number 42C555.
It is a primary and general object of the present invention to simplify and improve the operation of such disk storage system data path circuits.
It is another object of the present invention to provide such a mass storage system data path circuit that is optimized for both data and servo signals read from the storage media.